Of course it's wrong to steal parts, deliberately scratch paint, etc. And not letting it out of your sight is also good.
But I totally disagree with not letting kids (or adults for that matter) sit on and play with the tractor controls as long as you are present and explain and watch. That is a great education for the kids especially. If you are that touchy about your machine then you should keep it at home in your storage, and/or you probably spent too much money and time on your fix-up/paint-up.